Then there was the compensating migratory shift of the Hotland beasts--those which lived in the areas where the slanting rays of the Blue Sun could actually touch them, and which could not stand the, to them, terrible cold of the Darklands. Instead, they moved back and forth with the Blue Sun and remained in their own area--a hot, dry, fiery-bright hinterland occupied only by gnurrs, gpoles, and other horrendous beasts.

Beyond those areas, according to the robot patrols which had reconnoitered there, nothing lived. Nothing could. No protoplasmic being could exist under the direct rays of the Blue Sun. Even the metal-and-translite bodies of a robot wouldn't long protect the sensitive mechanisms within from the furnace heat of the huge star.

Each species had its niche in the World. Some, like the hurkle, lived in swamp water. Others lived in lakes and streams. Still others flew in the skies or roamed the surface or climbed the great trees. Some, like Dodeth's own people, lived beneath t

The intellectual joy of being "thrown in the deep end" and having to figure out an alien environment is delicious.

There is some commentary on the obvious solution to increasing population and decreasing farmland: build cities underground! By the end, most is made clear, especially with respect to the title. But it leaves some important things to the imagination.